lipid-a and Helicobacter-Infections

In this review, we discuss the findings and concepts underlying the "persistence mechanisms" of Helicobacter pylori (H. pylori), a spiral-shaped, Gram-negative rod bacterium that was discovered as a gastric pathogen by Marshall and Warren in 1984. H. pylori colonizes the gastric mucosa of nearly half of the human population. Infections appear in early childhood and, if not treated, persist for life. The presence or absence of symptoms and their severity depend on multiple bacterial components, host susceptibility and environmental factors, which allow H. pylori to switch between pathogenicity and commensalism. Many studies have shown that H. pylori components may facilitate the colonization process and the immune response of the host during the course of H. pylori infection. These H. pylori-driven interactions might result from positive or negative modulation. Among the negative immunomodulators, a prominent position is occupied by a vacuolating toxin A (VacA) and cytotoxin-associated gene A (CagA) protein. However, in light of the recent studies that are presented in this review, it is necessary to enrich this panel with H. pylori lipopolysaccharide (LPS). Together with CagA and VacA, LPS suppresses the elimination of H. pylori bacteria from the gastric mucosa by interfering with the activity of innate and adaptive immune cells, diminishing the inflammatory response, and affecting the adaptive T lymphocyte response, thus facilitating the development of chronic infections. The complex strategy of H. pylori bacteria for survival in the gastric mucosa of the host involves both structural modifications of LPS lipid A to diminish its endotoxic properties and the expression and variation of Lewis determinants, arranged in O-specific chains of H. pylori LPS. By mimicking host components, this phenomenon leaves these bacteria "invisible" to immune cells. Together, these mechanisms allow H. pylori to survive and live for many years within their hosts.

Topics: Adaptive Immunity; Animals; Antibodies, Bacterial; Carbohydrate Conformation; Gastric Mucosa; Helicobacter Infections; Helicobacter pylori; Host-Pathogen Interactions; Humans; Immunity, Cellular; Immunity, Mucosal; Killer Cells, Natural; Lipid A; Microbial Viability; Phagocytosis; Structure-Activity Relationship; Symbiosis; T-Lymphocytes

Helicobacter pylori, a Gram-negative bacterium, causes gastroduodenal inflammatory diseases such as chronic gastritis and peptic ulcers, and is also a risk factor for gastric carcinogenesis. In this article, we review recent developments and findings in the chemical synthesis and immunomodulatory activities of H. pylori lipid A and 3-deoxy-D-manno-2-octulosonic acid (Kdo)-lipid A, to clarify the structural basis for the inflammatory response to H. pylori LPS. The synthetic methods include a new divergent synthetic approach with a widely applicable key intermediate for other types of lipid A structures, as well as a selective α-glycosylation reaction between Kdo and lipid A. Cytokine induction assays of the chemically synthesized lipid A structures showed selective cytokine induction depending on the patterns of acyl groups and phosphate groups. The results of cytokine induction assay suggested that H. pylori LPS can modulate the immune response during infection, and also plays a role in chronic inflammatory responses.

Topics: Biological Assay; Cytokines; Glycosylation; Helicobacter Infections; Helicobacter pylori; Humans; Immunologic Factors; Leukocytes, Mononuclear; Lipid A; Microchemistry; Molecular Conformation; Structure-Activity Relationship; Sugar Acids

Lipopolysaccharides are generally considered toxic components of the Gram-negative bacterial outer membrane with potent immunomodulating and immunostimulating properties, but their contribution to adaptation of a given bacterial species to its microbial niche is, however, predominantly overlooked. Helicobacter pylori, as a cause of long-term infection in the gastroduodenal tract, has been proposed as a model for investigating and understanding the dynamics of bacterial persistence and parasitism in chronic infections. This review examines the structure and properties of H. pylori lipopolysaccharide and its lipid A moiety, and the insights that have been gained into their contribution to chronic infection and pathogenesis, including evasion and dampening of innate immune responses.

Topics: Helicobacter Infections; Helicobacter pylori; Humans; Lipid A; Lipopolysaccharides; Virulence Factors

Topics: Animals; Gastric Mucosa; Helicobacter Infections; Helicobacter pylori; Humans; Lewis Blood Group Antigens; Lipid A; Lipopolysaccharides

The present review describes the structure, attributes and properties of Helicobacter pylori lipopolysaccharides (LPS), and their potential role in pathogenesis. Although possessing certain attributes similar to those of LPS of other Gram-negative bacteria, H. pylori LPS possess unique biological properties. H. pylori LPS has, in general, low immunological activity and this property may aid the persistence of infection. The O-specific chain of the LPS mimics Lewis blood group antigens in structure. As these antigens are present in the gastric mucosa, the expression of Lewis antigens on the bacterial surface may camouflage the bacterium and aid survival of H. pylori. Alternatively, since autoantibodies against human antral gastric mucosa have been observed in H. pylori-positive patients, the relevance of LPS in the development of autoimmunity in H. pylori-associated disease requires further investigation. H. pylori LPS in part mediates the binding of the bacterium to laminin, and interferes with gastric cell receptor-laminin interaction, thereby potentially contributing to the loss of mucosal integrity. In vitro observations of inhibition of sulphated mucin synthesis and stimulation of pepsinogen secretion by LPS suggest new mechanisms for H. pylori-induced mucosal damage. Nevertheless, further in vivo studies are required to support their pathogenic role.

Topics: Helicobacter Infections; Helicobacter pylori; Laminin; Lewis Blood Group Antigens; Lipid A; Lipopolysaccharides; Mucus; Pepsinogens

Helicobacter pylori colonizes half of the global population and causes gastritis, peptic ulcer disease or gastric cancer. In this study, we were interested in human annexin (ANX), which comprises a protein family with diverse and partly unknown physiological functions, but with a potential role in microbial infections and possible involvement in gastric cancer. We demonstrate here for the first time that H. pylori is able to specifically bind ANXs. Binding studies with purified H. pylori LPS and specific H. pylori LPS mutant strains indicated binding of ANXA5 to lipid A, which was dependent on the lipid A phosphorylation status. Remarkably, ANXA5 binding almost completely inhibited LPS-mediated Toll-like receptor 4- (TLR4) signaling in a TLR4-specific reporter cell line. Furthermore, the interaction is relevant for gastric colonization, as a mouse-adapted H. pylori increased its ANXA5 binding capacity after gastric passage and its ANXA5 incubation in vitro interfered with TLR4 signaling. Moreover, both ANXA2 and ANXA5 levels were upregulated in H. pylori-infected human gastric tissue, and H. pylori can be found in close association with ANXs in the human stomach. Furthermore, an inhibitory effect of ANXA5 binding for CagA translocation could be confirmed. Taken together, our results highlight an adaptive ability of H. pylori to interact with the host cell factor ANX potentially dampening innate immune recognition.

Topics: Animals; Annexins; Gastric Mucosa; Helicobacter Infections; Helicobacter pylori; Humans; Lipid A; Lipopolysaccharides; Mice; Stomach Neoplasms; Toll-Like Receptor 4

Synthetic studies of lipid A and LPS partial structures have been performed to investigate the relationship between structures and functions of LPS. Recent studies have suggested several pathological implications of LPS from parasitic bacteria due to its influence on the host immune responses. To address this issue, we established an efficient synthetic strategy that is widely applicable to the synthesis of various lipid As by using a key disaccharide intermediate with selectively cleavable protecting groups. Porphyromonas gingivalis and Helicobacter pylori lipid As were synthesized and their biological activities were evaluated. All synthetic lipid As did not induce strong inflammatory responses: some are very weak cytokine inducers and others are antagonistic in IL-6 and IL-8 induction with E. coli LPS. On the other hand, P. gingivalis lipid As showed potent IL-18 inducing activity. Since IL-18 has been shown to correlate with chronic inflammation, P. gingivalis LPS may be implicated in the chronic inflammatory responses.

Topics: Bacteroidaceae Infections; Chemistry Techniques, Synthetic; Enzyme-Linked Immunosorbent Assay; Helicobacter Infections; Helicobacter pylori; Humans; Immunity, Innate; Immunomodulation; Interleukin-6; Interleukin-8; Lipid A; Lipopolysaccharides; Models, Chemical; Molecular Structure; Porphyromonas gingivalis

Cardiolipin (CL) is an anionic tetraacylphospholipid found in mammalian tissues, inner membrane of mitochondria and in the cytoplasmic membrane of Gram-positive and -negative bacteria. Lipid A is the principal structural component responsible for the range of biological activities of lipopolysaccharides. Here we report a MALDI-MS-based method for the sensitive simultaneous analysis of CL and lipid A from Helicobacter pylori cells. The sensitivity was demonstrated by the analysis of CL and lipid A from a single bacterial colony of in vitro grown H. pylori strain NCTC 11637 (ATCC 43504). We then characterized the CL and lipid A structures in H. pylori cells grown under three different conditions, on agar-horse blood plates, in liquid culture and ex vivo. The results revealed the presence of high amounts of myristic (C14:0) and 19-carbon cyclopropane (C19:0cyc) fatty acids. Alterations in CL structure were observed in H. pylori cells cultivated on plates as compared with the bacteria grown in broth culture. Furthermore, significant changes in lipid A acylation pattern were detected in H. pylori cells during formation of coccoids. In contrast, structural analysis of CL from ex vivo H. pylori cells recovered from the stomachs of infected Mongolian gerbils demonstrated only minor changes in acyl chain combination. This is the first report of simultaneous analysis of CL and lipid A from ex vivo cells of H. pylori.

Topics: Acylation; Animals; Cardiolipins; Fatty Acids; Gerbillinae; Helicobacter Infections; Helicobacter pylori; Lipid A; Sensitivity and Specificity; Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization

Both Helicobacter pylori and Campylobacter jejuni are highly prevalent Gram-negative microaerophilic bacteria which are gastrointestinal pathogens of humans; H. pylori colonizes the gastroduodenal compartment and C. jejuni the intestinal mucosa. Although H. pylori causes chronic gastric infection leading to gastritis, peptic ulcers and eventually gastric cancer while C. jejuni causes acute infection inducing diarrhoeal disease, the endotoxin molecules of both bacterial species contrastingly contribute to their pathogenesis and the autoimmune sequelae each induces. Compared with enterobacterial endotoxin, that of H. pylori has significantly lower endotoxic and immuno-activities, the molecular basis for which is the underphosphorylation and underacylation of the lipid A component that interacts with immune receptors. This induction of low immunological responsiveness by endotoxin may aid the prolongation of H. pylori infection and therefore infection chronicity. On the other hand, this contrasts with acute infection-causing C. jejuni where overt inflammation contributes to pathology and diarrhoea production, and whose endotoxin is immunologically and endotoxically active. Futhermore, both H. pylori and C. jejuni exhibit molecular mimicry in the saccharide components of their endotoxins which can induce autoreactive antibodies; H. pylori expresses mimicry of Lewis and some ABO blood group antigens, C. jejuni mimicry of gangliosides. The former has been implicated in influencing the development of inflammation and gastric atrophy (a precursor of gastic cancer), the latter is central to the development of the neurological disorder Guillain-Barré syndrome. Both diseases raise important questions concerning infection-induced autoimmunity awaiting to be addressed.

Topics: Animals; Autoimmune Diseases; Campylobacter Infections; Campylobacter jejuni; Carbohydrate Conformation; Carbohydrate Sequence; Endotoxins; Gangliosides; Guillain-Barre Syndrome; Helicobacter Infections; Helicobacter pylori; Humans; Lewis Blood Group Antigens; Lipid A; Molecular Mimicry; Molecular Sequence Data; Molecular Structure

Helicobacter pylori specifically takes up cholesterol and incorporates it into the bacterial membrane, yet little is currently known about cholesterol's physiological roles. We compared phenotypes and in vivo colonization ability of H. pylori grown in a defined, serum-free growth medium, F12 with 1 mg/ml albumin containing 0 to 50 mug/ml cholesterol.. While doubling times were largely unaffected by cholesterol, other overt phenotypic changes were observed. H. pylori strain SS1 grown in defined medium with cholesterol successfully colonized the stomach of gerbils, whereas SS1 grown without cholesterol failed to colonize. H. pylori lipopolysaccharide often displays Lewis X and/or Y antigens. Expression of these antigens measured by whole-cell ELISA was markedly enhanced in response to growth of strain SS1, 26695, or G27 in cholesterol. In addition, electrophoretic analysis of lipopolysaccharide in wild type G27 and in mutants lacking the O-chain revealed structural changes within the oligosaccharide core/lipid A moieties. These responses in Lewis antigen levels and in lipopolysaccharide profiles to cholesterol availability were highly specific, because no changes took place when cholesterol was substituted by beta-sitosterol or bile salts. Disruption of the genes encoding cholesterol alpha-glucosyltransferase or lipid A phosphoethanolamine transferase had no effect on Lewis expression, nor on lipopolysaccharide profiles, nor on the cholesterol responsiveness of these properties. Disruption of the lipid A 1-phosphatase gene eliminated the effect of cholesterol on lipopolysaccharide profiles but not its effect on Lewis expression.. Together these results suggest that cholesterol depletion leads to aberrant forms of LPS that are dependent upon dephosphorylation of lipid A at the 1-position. A tentative model for the observed effects of cholesterol is discussed in which sequential steps of lipopolysaccharide biogenesis and, independently, presentation of Lewis antigen at the cell surface, depend upon membrane composition. These new findings demonstrate that cholesterol availability permits H. pylori to modify its cell envelope in ways that can impact colonization of host tissue in vivo.

Topics: Animals; Cholesterol; Culture Media; Female; Gene Silencing; Gerbillinae; Helicobacter Infections; Helicobacter pylori; Lewis Blood Group Antigens; Lewis X Antigen; Lipid A; Lipopolysaccharides; Stomach

The cag pathogenicity island (cag PAI) genes are a major determinant of virulence of Helicobacter pylori (Hp). Lipopolysaccharide (LPS) purified from the cag PAI-positive (type I) strains induced apoptosis of primary cultures of guinea pig gastric mucosal cells. Lipid A catalyzed this apoptosis. These cells expressed the Toll-like receptor 4 (TLR4) mRNA and its protein, and type I Hp LPS phosphorylated transforming growth factor beta-activated kinase 1 (TAK1) and TAK1-binding protein 1 (TAB1) in association with up-regulation of the TLR4 expressions, suggesting that type I Hp LPS evoked distinct TLR4 signaling. In contrast, Hp LPS from type II strains with complete or partial deletion of the cag PAI genes did not phosphorylate TAK1 and TAB1 and failed to induce apoptosis. Accelerated apoptosis of gastric epithelial cells is one of the important events relevant to chronic, atrophic gastritis caused by Hp infection. The difference in proapoptotic action of LPS between the type I and II strains may support an important role of the cag PAI genes in the pathogenesis of gastric lesions caused by Hp infection.

Topics: Adaptor Proteins, Signal Transducing; Animals; Antigens, Bacterial; Apoptosis; Atrophy; Bacterial Proteins; Carrier Proteins; Drosophila Proteins; Epithelial Cells; Gastric Mucosa; Gastritis; Genotype; Guinea Pigs; Helicobacter Infections; Helicobacter pylori; Humans; Intracellular Signaling Peptides and Proteins; Lipid A; Lipopolysaccharides; MAP Kinase Kinase Kinases; Membrane Glycoproteins; Phosphorylation; Protein Processing, Post-Translational; Receptors, Cell Surface; Signal Transduction; Stimulation, Chemical; Toll-Like Receptor 4; Toll-Like Receptors